1. Field
This disclosure relates to transmission of packets across the public switched telephone network (PSTN), more particularly to conversion of a PSTN telephone call to transport a packet telephone call between two separate packet network domains.
2. Background
Currently, it is possible to place calls to the PSTN from a packet domain. The packet domain first must convert the packet to a proper format for transmission across the PSTN. For example, a packet voice call must be converted via the appropriate voice coder/decoder (codec). The data packets containing the data representative of speech are converted by a voice codec into a digitized stream of signals that can be reconstructed on the other send of the call into an audio signal. Coding of voice signals generally fall in the G.7XX family of codecs.
The International Telephony Union (ITU) has several different standards for coding of voice signals. Examples include G.711 voice coding at 64,000 bits per second (kbps) in a scheme referred to as Pulse Code Modulation (PCM), and G.726 using Adaptive Differential PCM (ADPCM). The specifics of these various standards are outside the scope of this disclosure. However the voice signal is coded, it will be decoded at the receiving end by a codec that uses the same standard resulting in an audio output to the listener.
If the PSTN is then connected to another packet network domain via a network gateway or other network device, unnecessary steps of coding at the sending end and decoding at the receiving end may occur. As can be seen in FIG. 1, the packet domain device 10 uses a PSTN converter 14 to converts the packets into the appropriate format for transmission across the PSTN. The receiving device 12, also a packet domain device, receives it in this PSTN format and then has to decode it and reconvert it back to packet format using PSTN converter 16. The sending device 10 had no way of knowing or discovering that the receiving device 12 is also a packet device, and therefore had to convert from packets to PSTN format for transmission. If it were possible for the sending device to discover the nature of the receiving device as a packet device, the coding and decoding for PSTN format would be unnecessary.